Mapping variations in local temperature and local power supply voltage that are present during operation of an integrated circuit

ABSTRACT

A method includes providing an integrated circuit (IC) having a plurality of oscillators at distributed locations in the IC, determining a respective rate of oscillation of each of the oscillators, and detecting variations in local temperature in the IC based on the determined rates of oscillation. Other embodiments are described and claimed.

BACKGROUND

During operation of an integrated circuit (IC) such as a microprocessor,there may be local variations in temperature and in the power supplyvoltage across the IC die.

Locations in the IC which experience higher temperatures than otherlocations are sometimes referred to as “hot spots” and may presentsignificant challenges to the system or systems provided to cool the ICduring operation. The issue of hot spots may compound the alreadysignificant demands placed on cooling systems by the ever increasingoperating rates and rates of power dissipation by microprocessors.

Moreover, the local increase in temperature at a hot spot may adverselyaffect the operating speed of components at the hot spot, potentiallycausing the IC to fail to meet the intended operating rate.

Also, hot spots may migrate from location to location on the IC die, asdifferent applications are executed. This further complicatesimplementation of designs to minimize hot spots.

Local variations in the supply voltage may also adversely affectoperation of an IC. The operating rate of components of the IC tends tobe reduced by localized reductions in supply voltage, potentiallyleading to overall failure of the IC due to, e.g., failing raceconditions.

During testing of an IC design, it would be desirable to obtainrelatively detailed, and substantially real-time, maps of localvariations in temperature and supply voltage, to aid in arriving atdesign solutions to mitigate and/or avoid the adverse consequences ofsuch variations. However, conventional techniques for detectingtemperature and supply voltage variations tend to be limited, expensive,time-consuming and/or unsatisfactory. For example, so-called V_(cc)sense pins on an IC package allow for detection of the local supplyvoltage level at a few locations on the IC die, but do not permit adetailed supply voltage map to be generated. Temperature maps may begenerated based on simulations, which may not be accurate, or based onempirical data obtained by Infra-red Emission Microscopy (IREM). Thelatter technique, though accurate, is disadvantageous in that it is verytime-consuming and involves destruction of the device under test (DUT).

Accordingly, improved techniques for mapping temperature and supplyvoltage variations on an IC die are needed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a somewhat schematic plan view of a microprocessor providedwith distributed sets of oscillators that are scannable for testpurposes in accordance with some embodiments.

FIG. 2 is a block diagram of a set-up provided according to someembodiments for testing of the microprocessor of FIG. 1.

FIG. 3 is a flow chart that illustrates a process that may be performedaccording to some embodiments using the test set-up of FIG. 2.

FIG. 4 is a flow chart that illustrates some details of a calibrationstage of the process of FIG. 3.

FIG. 5 graphically illustrates temperature-dependent variations inoscillating frequency of some of the scannable oscillators of themicroprocessor of FIG. 1.

FIG. 6 graphically illustrates temperature- and voltage-dependentvariations in oscillating frequency of one of the oscillators.

FIG. 7 illustrates one form of a temperature map that may be providedaccording to some embodiments.

FIG. 8 illustrates another form of a temperature map that may beprovided according to some embodiments.

FIG. 9 illustrates an example of a supply voltage map that may beprovided according to some embodiments.

FIG. 10 is a flow chart that illustrates a process performed accordingto some embodiments to detect a transient change in power supply voltageat a particular location in an IC.

FIG. 11 is a graphical representation of an integration window appliedaccording to some embodiments to oscillation data received from anoscillator in the microprocessor of FIG. 1.

FIG. 12 shows a waveform that represents a simulated transient change involtage that may occur at a particular location in the microprocessor ofFIG. 1.

FIG. 13 shows a waveform that represents a simulated signal that may bederived from oscillation data received from an oscillator in themicroprocessor of FIG. 1.

FIG. 14 shows a waveform that represents a simulated signal that isrecovered by post-processing from the signal illustrated in FIG. 13.

FIGS. 15–17 show respective waveforms that illustrate the effects ofrespective degrees of subsampling on the resolution at which a transientvoltage event signal may be recovered.

DETAILED DESCRIPTION

FIG. 1 is a somewhat schematic plan view of a microprocessor 20. In thisexample, the microprocessor 20 exhibits features of the well-knownPentium® microprocessor architecture produced by Intel Corporation, theassignee hereof.

It has been proposed to include in the circuitry of a microprocessor orother IC so-called process monitoring circuitry. An example of suchcircuitry is disclosed in U.S. Pat. No. 6,553,545, which is commonlyassigned herewith. Such circuitry is also sometimes referred to asIntra-Die Variation (IDV) probe circuitry, and may include groups ofoscillators at distributed locations in the IC die. For example, theremay be 98 clusters of 15 oscillators each provided in one examplemicroprocessor. Typically, each oscillator may be constructed as a ringoscillator. Each cluster may be referred to as a “fublet”, deriving itsname from the term “Functional Unit Block” or FUB. The oscillators ineach fublet may differ from each other in terms of such characteristicsas number of inverter stages, spatial orientation, and local transistorcharacteristics, to allow for detection of various types of processvariation. By design each fublet may contain an identical set ofoscillators, though differences in oscillator characteristics arisebetween the fublets as a result of process variations.

In addition to oscillators, each fublet may include a counter orcounters to record the oscillation rate of each oscillator. The fubletsmay be linked by a scan chain which allows the contents of the countersto be read out via a so-called test access port (“TAP”, not separatelyshown) of the IC. The respective frequencies of oscillation of theoscillators may be examined to obtain information about processvariations across the IC die. In other embodiments, a single counter maybe provided on the IC die to be shared by all of the oscillators tooutput count data seriatim for each of the oscillators.

Reference numeral 22 in FIG. 1 indicates a scan chain of the typereferred to in the previous paragraph, and the dots 24 (most notdirectly associated with a reference numeral) strung along the scanchain 22 each represent a respective fublet. Thus the dots along thescan chain 22 are indicative of the distribution of fublets on the IC20.

In accordance with various embodiments, it is now proposed that the IDVcircuitry also be employed to provide temperature and/or supply voltagemaps of the IC and/or to detect local supply voltage transient events(e.g., “droops”) during test operation of the IC and/or to detect longerterm voltage events (“sags”) during operation of the IC.

FIG. 2 is a block diagram of a test set-up 40 provided according to someembodiments for testing of the microprocessor 20, indicated as thedevice under test, or DUT (reference numeral 42), in FIG. 2. The testset-up 40 includes a processor 44, which may include one or moresuitably programmed microprocessors (not separately shown). Alsoincluded in the test set-up 40 is an input interface 46 which is coupledto the processor 44. A function of the input interface 46 may be tocouple to the test access port of the DUT 42 to receive oscillation ratedata from the scan chain 22 via the TAP. The oscillation rate data maybe indicative of a respective rate of oscillation of each one of atleast some of the oscillators (not separately shown) of the fublets 24.

The test set-up 40 may further include a control interface 48 coupled tothe processor 44. A function of the control interface 48 may be tocouple to the DUT 42 to cause the DUT to run one or more test programsor other programs, which may be stored in an exercise program store 50associated with the control interface 48. As will be appreciated bythose who are skilled in the art, causing the DUT to run one or moreprograms while in the test set-up may be referred to as “exercising” theDUT.

The test set-up 40 may also include a temperature control device 52,such as a conventional heat exchanger, to control the temperature of theDUT so that the DUT is at a temperature dictated by the processor 44.The temperature control device 52 is coupled to the processor 44 andoperates under the control of the processor 44.

In addition, the test set-up 40 may include a voltage control device 54which is coupled to the processor 44 and which operates, under thecontrol of the processor 44, to control the level of the power supplyvoltage (also referred to as “V_(CC)”) supplied to the DUT via a powerplane (not separately shown) of the DUT.

The test set-up 40 may further include one or more memory and/or storagedevices, collectively represented by a block 56 in FIG. 2. The device(s)56 may serve as program memory to store one or more programs to controloperation of the processor 44 in accordance with embodiments describedherein. In addition, the device(s) 56 may function as working memoryand, at various times during operation of the test set-up 40, may holdcalibration data 58 (to be discussed below) and oscillator frequencydata 60 gathered during testing of the DUT 42.

Also, the test set-up 40 may include various input/output devices (block62) coupled to and/or controlled by the processor 44. For example, theI/O devices 62 may include a conventional user interface including acolor computer display monitor, a keyboard and a mouse, as well as acolor printer to print out temperature and/or supply voltage maps asdiscussed below. (The specific I/O devices are not separately shown.)

FIG. 3 is a flow chart that illustrates a process that may be performedaccording to some embodiments using the test set-up 40.

Initially, as indicated at 80 in FIG. 3, the process may involve acalibration procedure, in which a respective temperature- andvoltage-dependent frequency function is determined for each one of aplurality of the IDV oscillators. The determination of such a functionfor an IDV oscillator will be referred to as “characterization” of theoscillator. In some embodiments, one oscillator is characterized in eachof the fublets during calibration. The oscillators selected forcharacterization may be essentially identical to each other, except forprocess variations experienced across the DUT during fabricationthereof. In other words, all of the oscillators selected forcharacterization may be designed to be identical.

In other embodiments, two oscillators (a pair of oscillators) may beselected from each fublet for characterization. The selected pair ofoscillators from each fublet may include a first oscillator and a secondoscillator which are expected, because of their respective designs, tohave significantly different frequency functions from each other. All ofthe “first” oscillators may be designed to be identical to each other,and all of the “second” oscillators may be designed to be identical toeach other (though different from the first oscillators, as notedabove).

FIG. 4 is a flow chart that illustrates some details of an examplecalibration procedure.

As indicated at 82 and 84 in FIG. 4, the level of V_(CC) applied to theDUT may be held fixed initially, and the temperature of the DUT may bevaried by operation of the temperature control device 52. For example,the temperature applied to the DUT may be varied in steps of 5° C. Thetemperature may be held at each step for a sufficient period to “soak”the DUT to thermal saturation, and while the temperature is being held,oscillation data may be read out from the scan chain 22 via the TAP ofthe DUT for each oscillator that is to be characterized, to measure thefrequency of the oscillator at the current temperature. The oscillationdata received via the TAP may be stored in the memory device(s) 56.

One issue that may require consideration in terms of temperature settingduring calibration is so-called “self-heating”, i.e., heating of the DUTas a result of power dissipated within the DUT during testing. Tominimize self-heating, it may be desirable to maintain the DUT in anidle state during calibration, e.g., a state with all core clocks in a“sleep” or standby mode. However, even in such a state, there may remaina significant amount of power dissipation due to leakage by the numeroustransistors that typically may be present in the DUT. As a result, theactual temperature at the DUT itself may be higher than the temperatureattempted to be set by using the temperature control device 52. However,it may be possible to measure the actual temperature by using a thermaldiode (not separately shown) that typically may be included at onelocation on the DUT. It may be desirable to use the actual measuredtemperature, rather than the temperature control device set point, incalculating the frequency function for the oscillators selected forcharacterization. Also, to minimize potential non-uniformity of theactual temperature across the DUT during calibration, it may bedesirable to limit the set point temperatures and the V_(CC) levelsapplied to the DUT during calibration.

Before, after or interspersed with the measurements made at varioustemperature steps, the temperature may be held fixed and the level ofV_(CC) applied to the DUT may be varied by operation of the voltagecontrol device 54, as indicated at 86 and 88 in FIG. 4. For example, thelevel of V_(CC) applied to the DUT may be varied in steps of 50 mV(e.g., in the vicinity of a typical V_(CC) level such as 1.4 V). WithV_(CC) at each step level, oscillation data may be read out from thescan chain 22 via the TAP of the DUT for each oscillator that is to becharacterized, to measure the frequency of the oscillator at the currentV_(CC) level. The oscillation data received via the TAP may be stored inthe memory device(s) 56.

Typically the IDV oscillators are such that changes in temperature orV_(CC) cause a linear change in oscillating frequency. For example, FIG.5 graphically illustrates temperature-dependent variations inoscillating frequency of some IDV oscillators, where each data line inFIG. 5 corresponds to a respective IDV oscillator, and all of theoscillators are designed to be identical, but are located in mutuallydifferent fublets. The divergence of slopes in the data lines will benoted and indicates differences in characteristics among the oscillatorsdue to process variations.

As indicated at 90 and 92 in FIG. 4, for each oscillator to becharacterized, a respective temperature- and voltage-dependent frequencyfunction may be calculated based on the oscillation data collected at 84and 88. The function for each oscillator to be characterized may takethe form:F=aT+bV+c,

where F represents frequency, a and b are respectively slope values fortemperature and voltage level derived from the oscillation data, c is alinear offset derived from the oscillation data, T representstemperature and V represents V_(CC) level. The values of a, b, and c maybe determined by fitting a plane to the data points generated at 84 and88.

FIG. 6 graphically illustrates temperature- and voltage-dependentvariations in oscillating frequency of one of the IDV oscillators.

Once the calibration procedure is complete, the test set-up 40 may beoperated to detect either or both of local variation in temperature andpower supply voltage in the DUT and/or to generate one or both oftemperature and voltage maps for the DUT. As used herein and in theappended claims, “temperature map” refers to a graphical representationof variation in local temperature relative to location on an IC die, and“voltage map” refers to a graphical representation of variation in powersupply voltage relative to location on an IC die.

Referring once more to FIG. 3, detection of local temperature variationsand generation of a temperature map will be described with reference toa left-hand branch 100 of the flow chart shown in FIG. 3. Initially inthe branch 100, as indicated at 102, the test set-up 40 may control theDUT 42 to run a suitable test application program. For example, the testapplication may be a conventional test program which tends to cause amaximum of power dissipation by the DUT. The test program may be run onthe DUT in a loop until the DUT reaches thermal and electricalequilibrium.

To eliminate the effect of local voltage sags, which are notquantifiable, the core clock(s) may be stopped and the DUT placed in asleep mode, as indicated at 104. The sleep mode may be maintained forabout one millisecond, which is not long enough to allow significantcooling of the DUT, but is likely to be long enough to allow overshootand ringing in the power supply to settle out. Then, approximately onemillisecond into the sleep mode, the oscillation data for thecharacterized oscillators may be read out via the scan chain 22 and theTAP of the DUT and may be received by the test set-up 40, as indicatedat 106. The respective frequencies (rates of oscillation) of thecharacterized oscillators may then be determined based on theoscillation data. Taking into account the current V_(CC) level appliedto the DUT, and the frequency function determined for each characterizedoscillator during calibration, a respective local temperature may becalculated for each fublet (as indicated at 108), thereby detectingvariations in local temperature in the DUT based on the respectivefrequencies of the characterized oscillators.

Next, as indicated at 110, the processor 44 may operate to generate atemperature map for the DUT based on the local temperatures calculatedat 108. One example of such a temperature map is shown in FIG. 7. InFIG. 7, a first horizontal direction axis 112 is indexed according tolocation on the IC die in a “Y” direction, a second horizontal directionaxis 114 is indexed according to location on the IC die in an “X”direction, and the vertical direction axis 116 represents temperature.Note that the mapping 118 indicates a local increase in temperature ofsome 20° C. at the right-hand side of the die at around 4000 microns inthe Y direction. This corresponds to the locus of a high-speed executionunit of the IC.

FIG. 8 shows another example of a temperature map that may be generatedaccording to some embodiments based on the local temperatures calculatedat 108. In the drawing, the small black squares (some indicated byreference numeral 120) represent the locations of the fublets on the ICdie, and the different kinds of shading, which may be represented bydifferent colors in some embodiments, are indicative of the varyinglocal temperatures.

The temperature maps of FIGS. 7 and/or 8 may be displayed on a displaycomponent of the test set-up 40 and/or printed out by a printer of thetest set-up 40.

In some embodiments, a “motion picture” presentation of localtemperature variations may be generated from a sequence of temperaturemaps (like, e.g., the temperature map of FIG. 8) to aid in analyzingissues such as the thermal time constant of the DUT and/or hot spot tocold spot differential temperatures. To form such a motion picturepresentation, successive temperature maps may be generated at timeintervals while exercising the DUT. For example, the DUT may be placedin a low power mode for one second and the oscillator data may then becollected to generate a first temperature map. Next, the DUT may becaused to run a maximum power application for one complete set offunctional instructions, and then oscillator data may be collected againto generate another temperature map. The DUT may then be caused to runthe maximum power application in an infinite loop, and oscillator datamay be collected at 1 millisecond intervals during this time to generatefurther temperature maps for the motion picture presentation. Theinfinite loop execution of the maximum power application and thecollection of oscillator data may continue until the DUT reaches athermal equilibrium. For example, where the DUT is an IC that ispackaged with an integrated heat spreader (IHS), reaching thermalequilibrium may take five to seven seconds. On the other hand, where theDUT is a bare die, only one or two seconds may be required to reachthermal equilibrium.

The motion picture presentation of the thermal mapping data may beprovided on a display component of the test set-up 40.

A motion picture presentation of temperature maps for the DUT, or evenstatic temperature or supply voltage maps, may be of significant valueand interest to engineers charged with functions such as IC design,debug, assembly, quality and reliability.

Referring once more FIG. 3, detection of local variations in powersupply voltage, in a process illustrated in a right-hand branch 130 ofthe flow chart of FIG. 3, may be performed in addition to or instead ofthe detection of temperature variations described above.

Initially in the branch 130, as indicated at 132, the test set-up 40 maycontrol the DUT 42 to run a suitable test program. For example, the testprogram may be the same type of maximum power application referred toabove in connection with branch 100 in FIG. 3. As another example, thetest program may be one that exercises a particular fublet (e.g., aprogram to cause high speed execution on a floating point calculationunit.)

With the test program running on the DUT, oscillation data for thecharacterized oscillators is read out via the scan chain 22 and the TAPof the DUT at a first point in time (e.g., at a specific stage ofexecution of the test program) at which it is desired to detect localvariations in power supply voltage. The oscillation data is received bythe test set-up 40, as indicated at 134, and is stored in, e.g., thememory device(s) 56. Immediately after reading out the oscillation dataat the first point in time, the execution of the test program is stopped(as indicated at 136) and the phase-locked loop (PLL) clocks in the DUTare stopped, to substantially eliminate local voltage level variationsin the power plane of the DUT. Then, at a second point in time that isshortly after the stopping of the PLL clocks, oscillation data for thecharacterized oscillators is read out once more via the scan chain 22and the TAP of the DUT and is received by the test set-up 40, asindicated at 138. It may be desirable for the second point in time to belong enough after the stopping of the PLL clocks to allow oscillationsin the power supply voltage level to settle out, but not so long as toallow for a significant change in the local temperatures in the DUT. Forexample, the second point in time may be about 500 microseconds afterthe stopping of the PLL clocks. The oscillation data received at thesecond point in time may also be stored in the memory device(s) 56.

Since the PLL clocks are stopped at the second point in time, it may beassumed that the local power supply voltage level is known for all ofthe characterized oscillators. Consequently, as indicated at 140, arespective local temperature at each of the characterized oscillatorsmay be calculated in the same manner as described above in connectionwith 108, above. These local temperatures, determined as of the secondpoint in time, may also be assumed to have been present at the firstpoint in time. Thus the influence of local temperature variations on theoscillation data collected at the first point in time is known, and, asindicated at 142, the respective local power supply voltage level ateach of the characterized oscillators may be calculated based on therespective local temperature determined at 140 and based on therespective frequency of the characterized oscillator as determined basedon the oscillation data collected at the first point in time.

Next, as indicated at 144, the processor 44 may operate to generate asupply voltage map for the DUT based on the variations in local powersupply voltage determined at 142. One example of such a supply voltagemap is shown in FIG. 9. Again, the small black squares (some indicatedby reference numeral 120) represent the locations of the fublets on theIC die. The different kinds of shading in FIG. 9, which may berepresented by different colors in some embodiments, are indicative ofthe varying local supply voltage levels.

The voltage map of FIG. 9 may be displayed on a display component of thetest set-up 40 and/or printed out by a printer of the test set-up 40.

In the examples given above, one oscillator in each fublet may becharacterized and thereafter used for thermal and voltage mapping. Inother embodiments, a pair of oscillators in each fublet may becharacterized and thereafter used for thermal and voltage mapping. Eachpair of oscillators may include a first oscillator and a secondoscillator which may be considered “adjacent” to each other in the sensethat both are co-located in the same fublet. The first oscillator ofeach pair may have a temperature- and voltage-dependent frequencyfunction (determined during calibration) that has a first slope, and thesecond oscillator of each pair may have a temperature- andvoltage-dependent frequency function (also determined duringcalibration) that has a second slope that is substantially differentfrom the first slope. For example, the first slope may incline in adifferent direction from the second slope (one positive and the othernegative) and/or the respective magnitudes of the two slopes may besubstantially different. All of the first oscillators of the pairs ofoscillators may be designed to be identical (though subject to processvariations) and all of the second oscillators of the pairs ofoscillators may be designed to be identical (though subject to processvariations).

After calibration (which may be in accordance with the process of FIG.4), oscillator data indicative of temperature and voltage variations maybe collected in a single pass at a particular point in time duringexecution of a program of interest. Since two contrasting characterizedoscillators are available for frequency measurement in each fublet, thedata indicative of F₁ (frequency of the first oscillator) and F₂(frequency of the second oscillator) is available for each fublet, andmakes it possible to solve the simultaneous equations:F ₁ =a ₁ T+b ₁ V+c ₁F ₂ =a ₂ T+b ₂ V+c ₂for T and V at each fublet.

It may also be desirable to use IDV oscillator frequency information todetect short-duration fluctuations (e.g., transient changes) in localpower supply voltage levels. Because the frequency information iseffectively integrated by being measured via a counter at the fublet,there may be limitations on detection of short-duration events.

For example, consider an IDV oscillator that runs at 8 GHZ. Thisfrequency may be pre-scaled by a certain factor before being measured bythe counter. If the pre-scaling factor is 128, the counter would reporta (scaled) frequency of 62.5 MHz, so that each cycle has a duration of16 nanoseconds.

Next suppose that a droop event to be captured has a duration of 5nanoseconds. The number of cycles in the droop event would be 312.Assuming that the droop causes a 5% shift in the scaled frequency,resulting in a reduction from 62.5 MHz to 59.3, the corresponding cyclecount from the counter would drop to 296. If the magnitude of the droopwere 100 mV, this would translate to a sensitivity of 31 mV/MHz with aminimum resolvable voltage difference of 6.2 mV.

In some alternative designs of the DUT, the pre-scaling factor may be 64rather than 128. In such a case, the resolution limit would be doubledto 3.1 mV. In still other designs, pre-scaling factors of 32 or 16 maybe implemented to further increase resolution. There may be, however,trade-offs involved in providing lower pre-scaling factors, since thesize of the counter may need to be increased to accommodate the higherfrequencies to be reported by the counters with lower pre-scalingfactors.

Typically, it may be necessary for an IDV oscillator to run for 20microseconds or more to permit accurate measurement of the oscillator'sfrequency. Consequently, a voltage level event that lasts, say, onemicrosecond will tend to be “washed out” by the integration involved inthe frequency measurement. Also, the magnitude of the event may tend tobe distorted as a result of being averaged over the integration window.To mitigate this filtering effect and improve the resolution, it may bedesirable to employ a dithering technique that is akin to thosedescribed in the following articles: A. S. Fruchter et al., “A novelimage reconstruction method applied to deep Hubble Space Telescopeimages”, arXiv:astro-ph/9708242v1, 26 Aug. 1997; Tod R. Lauer,“Combining undersampled dithered images”, arXiv:astro-ph/9810394v1, 23Oct. 1998; A. S. Fruchter et al., “Drizzle: a method for the linearreconstruction of undersampled images”, arXiv:astro-ph/9808087v2, 19Oct. 2001.

More specifically, multiple “snapshots” (readouts of oscillation data)may be taken, each slightly offset in time from the others, toreconstruct the original voltage droop waveform. In other words, theintegration time window may be shifted across the droop temporal profilein steps that are some small fraction of the window duration. Forinstance, if the counter integration window were five microseconds, and5×“subsampling” were desired, the step size would be equal to onemicrosecond. Where a droop event is captured in oscillation data, theIDV oscillator data frames in the time domain may be regarded as theconvolution of the integration window profile and the voltage droopprofile.

Let the window function be expressed as sx(t), and let the droop profilebe expressed as sy(t). Then the voltage mapping data frames are theconvolution of the sx(t) and sy(t) datasets. The convolution is theproduct of the respective functions in the Fourier domain, and may berepresented as:conv(t)=sx(t){circle around (x)}sy(t)=ℑ⁻¹[ℑ(sx(t))×ℑ(sy(t))].To extract the unknown voltage droop profile sy_(ext)(t) from theconvolution, the known window profile is divided into the convolution inthe Fourier domain, as indicated below:

${{sy}_{ext}(t)} = {{{??}^{- 1}\left\lbrack \frac{{??}\left( {{conv}(t)} \right)}{{??}\left( {{sx}(t)} \right)} \right\rbrack}.}$

FIG. 10 is a flow chart that illustrates a process that may be performedaccording to some embodiments to recover a droop event profile from IDVoscillation data. Initially, as indicated at 160, a calibrationprocedure may be performed, such as the procedure described above withreference to FIG. 4. Next, as indicated at 162, the oscillation data“snapshots” are taken. That is, a respective rate of oscillation of thecharacterized oscillator at the location of interest is detected at eachof a sequence of points in time. The duration of the intervals betweenthe points in time depends on the degree of “subsampling” that isdesired. The function indicated by the set of samples produced by thesnapshots is then divided in the Fourier domain by a function whichcorresponds to the counter integration window function (as indicated at164), and from this result the waveform for the droop in voltage eventis generated (as indicated at 166). In this way, a droop event or othertransient change in local power supply voltage may be detected based onthe respective rates of oscillation of the characterized oscillator atthe sequence of points in time.

FIGS. 11–14 graphically illustrate aspects of the process of FIG. 10.FIG. 111 shows a simulated integration window profile in the timedomain. FIG. 12 shows a simulated example droop profile to be detected,assumed to be a —sinc(t) function. FIG. 13 shows the convolution of thewaveforms of FIGS. 11 and 12, and thus represents a simulated functionindicated by the snapshot data. FIG. 14 shows a simulated waveform of adroop event profile as recovered from the snapshot data using theprocess of FIG. 10. Note the distortion and aliasing at the edges of thewaveform of FIG. 14, resulting from the original sinc(t) function beingtruncated in the evaluation.

FIGS. 15–17 illustrate the varying effects of the degree of subsamplingemployed upon the resolution obtained for the recovered droop profilewaveform. FIG. 15 shows a simulated recovered droop profile waveformwhen 4× subsampling is employed; FIG. 16 shows a simulated recovereddroop profile waveform when 8× subsampling is employed; FIG. 17 shows asimulated recovered droop profile waveform when 16× subsampling isemployed. In general, as the subsampling shift step becomes a largerpercentage of the window duration, the fidelity of the recovered profilewaveform is degraded as higher frequency information is lost. It may bedesirable to select a sub-sampling rate that is critically sampled atleast twice the highest temporal frequency component that is to bedetected. For example, to detect a voltage droop event having a durationof about one microsecond using a 10 microsecond time window, it may bedesirable to employ a sub-sampling rate of 20× or higher.

The thermal and voltage mapping described herein and/or the detection oftransient voltage events, may allow for improved IC debuggingprocedures. For example, the thermal mapping described herein may be anattractive alternative to examination by IREM, since the thermal mappingdescribed herein does not require such difficult and time-consumingsteps as removal of a heat spreader and thinning of the IC die. In someembodiments, the thermal mapping described herein may take as little ason the order of ten minutes.

The thermal mapping techniques described herein may also be moreaccurate for determining the thermal resistance and non-uniform thermalimpedance of a packaged die than conventional techniques which employthermal replicas of an IC die.

The thermal mapping techniques described herein may also be lesstime-consuming and expensive for detecting voids in the thermalinterface material that couples the IC die to a heat spreader, ascompared to a conventional techniques such as c-mode scanning acousticmicroscopy (CSAM). Since only a differential measurement may be neededrather than absolute temperature results, it may be possible to foregothe calibration procedure described herein.

The process for detecting voids may involve, first, measuring the IDVoscillator frequency for a given type of oscillator at each fublet at avery low applied voltage, just enough for the DUT to be functional. Thelow voltage level may be employed to reduce self-heating and to reducethe effects of leakage. Then the DUT may be subjected to very highvoltages just below the burn-in voltage. The DUT may then be subjectedto a near uniform heating pattern such as PLL warm up, or if the DUT hassufficient leakage, may be allowed to self-heat long enough to reach asteady state. Achievement of the steady state may be monitored via thethermal diode.

Once the DUT has reached the steady state, the voltage may be reducedsuddenly to the initial low voltage. After a predetermined period ofdelay, long enough for voltage droops to settle, but not enough fortemperature to change significantly, another measurement of the IDVoscillator frequency of the selected oscillators may be performed. Thepresence of voids may be detected by comparing the two IDV measurementswith a standard profile of uniform power.

The voltage mapping technique described above may be applicable tospeed-path debugging. With the voltage mapping technique describedabove, a debugging engineer may be able to observe voltage across thepower plane of the DUT at the point in time that a failure occurs duringspeed-path debugging. The debugging engineer may then be able to detectvoltage anomalies at the point of failure, and to address the anomalieswith power-delivery design alternatives or other steps.

The temperature and voltage mapping techniques described herein mayeliminate any need for finite element analysis or simulation orextrapolation, and are non-destructive, non-intrusive and do not requiresample preparation. Moreover, the temperature and voltage mappingtechniques described herein, as well as the voltage event detectiontechnique described herein, may promote less difficult, less timeconsuming and more effective design, validation and testing of ICs, suchas microprocessors. Further the techniques described herein may notentail major costs. The components of the test set-up described herein,such as the temperature control device and the interface to the DUT TAP,may not require large expenditures.

The techniques described above also may not be limited to relatively lowtemperature and/or relatively low frequency applications, as is the casewith IREM examination.

In general, the techniques described herein may allow design, debug,test, reliability and validation engineers to increase theirunderstanding of operating characteristics of ICs, thereby improving andfacilitating the design process. In addition, yields and frequencybinning for IC production may be improved with the information availablefrom temperature and voltage mapping as described herein. Also, thethermal mapping described herein may aid in design of thermal managementand power delivery systems for microprocessors and other ICs.

In embodiments described above, the data indicative of the oscillationrate of the oscillators has been read out from the DUT in the form of adigital count provided by a counter or counters on the DUT.Alternatively, however, an analog oscillation signal provided by anoscillator may be taken off from the die of the DUT and then processedoff-die to yield oscillation rate data for the oscillator.

Although the embodiments described herein have been presented in thecontext of a microprocessor, it should be understood that the techniquesdescribed herein are also applicable to other types of ICs. The numberof fublets from which IDV oscillator data may usefully be gathered mayvary according, e.g., to the type of IC, and may range, for example,from 5 or 25 or 50 or more to upwards of 100.

In embodiments described above, detection of local temperature and/orsupply voltage variations based on IDV oscillator frequencies has beenapplied in a test and/or design context. In addition, or alternatively,IDV oscillator frequencies may be detected and used to determine localand/or die-wide temperature and/or supply voltage conditions when the ICis installed in an end user device. For example, such temperature and/orsupply voltage data may be used to control cooling systems and/or powersupply systems in the end user device during operation of the end userdevice.

The several embodiments described herein are solely for the purpose ofillustration. The various features described herein need not all be usedtogether, and any one or more of those features may be incorporated in asingle embodiment. Therefore, persons skilled in the art will recognizefrom this description that other embodiments may be practiced withvarious modifications and alterations.

1. A method comprising: providing an integrated circuit (IC) having aplurality of oscillators at distributed locations in the IC; determininga respective rate of oscillation of each of the oscillators; detectingvariations in local temperature in the IC based on the determined ratesof oscillation; and performing a calibration procedure prior to thedetermining, the calibration procedure comprising: determiningrespective rates of oscillation of the oscillators at varioustemperatures applied to the IC; and determining respective rates ofoscillation of the oscillators at various voltages applied to the IC. 2.The method of claim 1, wherein the oscillators are ring oscillators. 3.The method of claim 1, wherein the plurality of oscillators include atleast 5 oscillators.
 4. The method of claim 3, wherein the plurality ofoscillators include at least 25 oscillators.
 5. The method of claim 4,wherein the plurality of oscillators include at least 50 oscillators. 6.The method of claim 3, further comprising: generating a temperature mapfor the IC based on the detected variations in local temperature.
 7. Amethod comprising: providing an integrated circuit (IC) having aplurality of oscillators at distributed locations in the IC, said ICbeing a microprocessor; determining a respective rate of oscillation ofeach of the oscillators; detecting variations in local temperature inthe IC based on the determined rates of oscillation; running anapplication program on the IC; and after running the applicationprogram, placing the IC in a sleep mode; and wherein the determining isperformed with the IC in the sleep mode.
 8. The method of claim 7,wherein the determining includes receiving data from a test access portof the IC.